trying to convert a hack need help plz

noob at this im trying to alter a top posters hack for display on seperate page to show top thread starters in specific forums

im sure the line that needs changing is this

PHP Code:

$postsresult = mysql_query("SELECT username,posts,userid FROM user $exn ORDER BY posts desc LIMIT 0,$maxposters") or die("Unable to complete query"); 

but after a lot of attempts im now at a loss wat to do

ne help will be gr8ly appreciated

everything iv tried has resulted in the message unable to complete query